Producing petroleum from a subsurface formation



Feb. 4, 1964 D. L. HOYT PRODUCING PETROLEUM FROM A SUBSURFACE FORMATION Filed July 2, 1958 United States Patent O 3,126,263 PRODUCING PETROLEUM FROM A SUBSURFACE FORMATION Donald L. Hoyt, Houston, Tex., assigner to Texaco Inc., a corporation of Delaware Filed July 2, 1958, Ser. No. 746,285 1 Claim. (Cl. 16S-21) This invention relates to the recovery and production of petroleum from a subsurface petroleum-producing formation. In accordance with one embodiment this invention relates to the recovery and production of petroleum from a subsurface petroleum-containing formation employing an operation wherein a well bore is employed both as a gas injection well and as a petroleum production well.

One of the most efficient methods of displacing petroleum from a subsurface petroleum-producing formation, particularly a formation having considerable structural relief, is the injection of gas high in the formation, near the top or crest, and producing oil from near the bottom of the formation or lower portion thereof. By operating in this fashion advantage is taken of the natural segregating effect of gravity. There are many formations, however, which possess relatively little structural relief or dip. ln the production of petroleum from such formations by injection of gas into the upper portion thereof a multitude of injection wells is required so that the injected gas is forced evenly downwardly, in a blanket-like manner, into the petroleum-producing formation while producing petroleum from the lower portions thereof so that during the :gas injection and petroleum production operations advantage may be taken of the segregating effect of gravity. As indicated, however, this method involves the employment of very many wells and, consequently, in most instances is economically prohibitive.

lt is an object of this invention -to provide an improved method for the recovery and production of petroleum from a subsurface petroleum-producing formation.

Another object of this invention is to provide an improved method of recovering and producing petroleum from a subsurface petroleum-producing formation involving operations wherein the same well bore penetrating the petroleum-producing formation is employed as a gas injection well and as a petroleum production well.

Another object of this invention is to provide a method wherein a petroleum-producing formation can be produced by the injection of gas into the upper portion thereof while petroleum is being produced from the `lower portion thereof, and wherein premature lingering or short circuiting of the injected gas from the upper portion of the formation into the lower portion of the formation in the vicinity of the well bore during the petroleum production operation is inhibited and/ or obviated.

Yet another object of this invention is to provide a method for the production of petroleum from subsurface petroleum-producing formations having relatively little s 'uctural relief or dip.

Still another object of this invention is to provide a method of producing petroleum from subsurface petroleum-producing formations involving operations wherein advantage is taken of the segregating effect of gravity.

How these and other objects of this invention are accomplished will become apparent in the light of the accompanying disclosure and drawing wherein there is schematically illustrated a petroleum production operation carried out in accordance with the practice of this invention. ln at least one embodiment of the practice of this invention at least one of the foregoing objects will be achieved.

In accordance with this invention an improved method of recovering and producing petroleum from a subsurface ice petroleum-containing formation is accomplished by sealing off an upper portion of the petroleum-producing formation to create a substantially fluid or gas impermeable zone therein in the vicinity of the well bore, followed by the injection of gas into the upper portion of the formation at a location above the aforesaid gas impermeable zone and producing petroleum from the lower portion of the formation beneath the aforesaid iluid or gas impermeable zone within the upper portion of the formation.

Various methods may be employed in the practice of this invention for the creation of a gas impermeable zone in the upper portion of the formation prior to the injection of gas into the formation above said zone. One method particularly suitable for use in the practice of this invention involves fracturing the petroleum-producing formation in lthe upper portion thereof to create a substantially horizontal fracture, such as a fracture extending substantially horizontally, radially outwardly from the well bore. The resulting fracture is then treated in such a manner as to render the fracture and that portion of the formation immediately encompassing the fracture substantially gas impermeable. Suitable methods -for rendering a permeable formation or fracture substantially gas impermeable include cementing wherein cement is forced into the fracture and permitted to set therein with the resultant creation of a huid impermeable zone and fracture. Desirably, a fluid cement may be employed as the fracturing iiuid with the result that upon completion of the -fracturing operation the fracture is occupied by the cement which subsequently sets up therein to an impermeable mass. Another method of creating a substantially fluid or gas impermeable zone within a subsurface petroleum-producing formation, without the necessity of creating a fracture therein, involves the injection into the formation of a iluid or liquid cement or liquid plugging agent which permeates the formation in the Zone of injection and eventually sets up therein, per se, or by the subsequent addition of a treating agent. Other methods of creating a substantially iiuid impermeable zone or barrier within a petroleum-producing formation are known.

Any gas may be suitably employed as a pressure gas in the practice of this invention. Desirably, however, the gas injected into the petroleum-producing formation, above the fluid or gas impermeable zone created therein, is natural gas, preferably gas recovered from the formation undergoing treatment. Natural gas comprises a major amount of methane and minor amounts of ethane, propane and butane. Accordingly, any of the aforesaid normally gaseous hydrocarbons, alone or in any suitable admixture, may be suitably employed in the practice of this invention as the pressuring gas. Other suitable pressuring gases include flue gas, carbon dioxide, carbon monoxide, air, nitrogen, etc.

The substantially fluid or gas impermeable zone created within the upper portion of the petroleum-producing formation extends substantially horizontally, outwardly, radially lfrom the well bore for a considerable distance, such as a distance in the range lil-200 feet, more or less. Preferably the outer periphery of the -uid impermeable zone created within the petroleumproducing formation is sufciently distant from the well bore and the lower portion of the formation wherefrom petroleum -is produced so that the buoyancy effect, exerted upon the gas injected into the upper portion of the formation, due to the density difference between the gas and the denser liquid petroleum therein, is at least as great as or greater than the pressure differential, exerted upon an increment of gas at the outer periphery of the zone, resulting from the Aiow of petroleum into the well bore in the lower portion of the formation `during the petroleum-producing operation. ln other words, the injected gas which reaches the router periphery of the zone will not be drawn downward directly but will occupy the upper portion of the formation and descend in blanketlike fashion to displace petroleum into the lower portion of the formation.

Referring now in detail tothe accompanying drawing which schematically illustrates an embodiment of the practice of this invention wherein natural gas is injected into the upper portion of the formation While petroleum is produced from the lower portion of the formation, the vgas being injected linto and the petroleum being produced via the same lwell bore, a wellV bore 11 is shown penetrating petroleum-producing formation 12. The well bore is provided wvith casing 14. In accordance with this invention, as illustrated in the drawing, a fracture 15 extending'substantially horizontally and radially out- V Wardly from well bore 11 is created within the petroleumproducing formation 12 in the upper portion thereof and filled with Vcement 15 permitted to set therein with the resultant creation of a substantially fluid impermeable pancake-shaped zone surrounding the well bore 11.

There .is provided within the well bore 11, substantially concentric with respect to casing 14 therein, production tubing 16. In the annular space between production tubing 16 and casing 14, above the cement filled fracture 15, there is positioned a packer 1S made of suitable expansible material. The packer -18 serves to make a uidti-ght seal between casing 14 and production tubing 16. Following the setting of packer 18 natural gas, methane, supplied from a suitable source at the sur-face via conduit 19 is injected into the annular space between casing 14 and tubing 16. The thus-injected gas Vflows down the annulus between casing 14 and tubing -16 and outwardly into the upper portion of petroleum-producing formation 12 via perforations Ztl at a location above cement filled fracture 15. As the gas is injectedinto the upper portion lof the lformation above the fluid impermeable cement iilled .fracture 15, or subsequently thereto, continuously or intermittently petroleum is produced from the lower portion of formation 12 via perforations 21 provided in the lower end of casing 14. The resulting produced petroleum moves upwardly within production tubing 16 and is produced at the surface via conduit 22.

VIn laccordance with theY foregoing operations injected the formation l12 are insuicient to cause short circuit-` ing or by-passing of the injected gas downwardly along the Well bore 11 into penforations 21. As a result the injected gas tends to vfollow the contour lines within the producing formation 12 and migrates inra blanket-like manner downwardly within formation 12 displacing the hydrocarbons. It is to be noted also that the substantially fluid or gas impermeable zone within the upper portion of the formation 12, created by the cement `filledV fracture `15 therein, positively prevents any short circuiting or by-passing of the injected gas downwardly along -well bore 11 in the direction of production perforations 21.

One or more of the aforesaid operations may be carried out consecutively with respect to the same AWell bore. For example, when it is found that the injected gas is entering production perforations 21 in excessive amounts, the formation :may be again'treated or fractured, and a fluid-.impermeable zone created therein in the zone of the formation adjacent perforations 21,-b-ut below these perforations. Vlf these perforations `21y are not needed to achieve the desired gas injection capacity they should be sealed otf, `and gas injection maintained through perfor tions `20 into formation 12.` Petroleum production is re- Y surned from an even lower portion of formation 12 via other perforations, not illustrated.

As will be apparent to those skilled in the many alterations, imodifcations and changes may be made in the practice of this invention .in the ylight'of the accompanying disclosure rwithout departing from the spirit or scope of this invention.

II claim:

A method of producing petroleum via a well bore penetrating a subsurface petroleum-producing formation having a substantial thick-ness which comprises fracturing .said formation at a location below the top and in the upper Ifraction of said formation to create a substantially horizontal fracture therein extending radially outward .from said well bore, cementing the resulting fracture to render the same substantially gas irripermeableA thereby dividing said formation into an upper portion and a lower portion adjacent said Well bore, dividing said well bore into an upper portion and a lower portion by setting a packer having production tubing extending therethrough above andV adjacent said fracture and below the top of said formation, introducing a non-oxidizing gas under pressure via said upper portion of said well bore into said upper portion of said formation above the location of said 'fracture therein, and producing petroleum from said lower portion of said well bore from said lower portion of said formation via saidl production tubing in said welll bore.

References Cited in the le of this patent UNITED STATES PATENTS .Y

2,368,424 Reistle Jan. 30, 1945 2,693,497 Spearow Apr. 22, 1952 2,749,988 West June `12, i956 2,767,792 Spearow Oct. 23, 1956K 2,874,777 Tadema Feb. 24, 1959 t i l. 

